s = 0
count = 0

f =  open('input.txt', 'r') # r - read, w - write

while True:
    st = f.readline().strip()
    
    if not st:
        break
    s += int(st)
    count += 1
f.close()

fw = open('output.txt', 'w')
fw.write(str(s / count))
fw.close()
